我怎样才能知道Postgres中有多大的一个大型文本字段?

I'm storing some large XML documents in TEXT fields in Postgres and I'm trying to find out how efficiently TOAST is compressing them. I've got a 2.2mb XML doc that is able to be zipped down to 51kb so I want to understand how close the compression ratio of TOAST can match it to make a final decision on how I'll be archiving these documents over time.I'm storing some large XML documents in TEXT fi